Cold-finished steels and method for manufacturing same



COLD-FINISHED STEELS AND METHOD FOR MANUFACTURING SAME Elliot S.'Nachtman, ParkForest, Ill., assignor to La Salle Steel Co., Hammond, Ind., a corporation of Delaware No Drawing. Application october 22, 1956 Serial No. 617,264"

7 Claims. (Cl. 148-12) This invention relates to a new: and improved metallurgical process for improvingphysical and mechanical properties of steel, and it relates more particularly to a process capable of use in the cold-finishing of steel to improve physical and mechanical properties of the steel.

This invention constitutes a modification over the processes described in the copending applications Serial No. 518,411, Serial No. 518,412, SerialNo. 518,413, and Serial No. 518,414, filed June 27, 1955, now Patents No. 2,767,837, No. 2,767,835, No. 2,767,836 and No. 2,767,838, respectively.

It is an object of this invention to produce and to provide a method for producing steel products having improved mechanical. and physical properties.

Another object of this invention is to provide a method which has application in the cold-finishing of steels wherein the properties and characteristics of the steels are materially changed toincrease the uniformity of properties and characteristics of steels of, corresponding chemistry from heat to heat, to expand the range of physical and mechanical properties capable of being developed in the steels, to modify the combinations of physical and mechanical properties in steel thereby to produce steels capable of use in specific applications, and to produce steel products having new and improved characteristics and physical and mechanical properties of greater value.

In the aforementioned copending applications, the inventive concepts reside in a method for the improvement of physical and mechanical properties of steel by the processing of the steel in an elevated-temperature-reduc tion step, wherein, for example, the steel is advanced through a die to take a reduction in cross-sectional area ,while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition or a temperature of about 1l00-1200 F. Depending upon the temperature at which the steel is advanced through the die, various physical and mechanical properties can be markedly changed by comparison with the same steels, given an equivalent reduction by advancement of the steel through an equivalent die but while the steel is at ambient temperature. Thus, by controlling the temperature of the steel advanced through the die and by the control of chemistry and the amount of reduction, it has been made possible, in a cold finishing operation, as the term is used in the trade, to produce steel products having new and improved physical and mechanical properties and other characteristics not heretofore available in steels fabricated by other means.

In a number of copending applications filed concurrently herewith, description is made further of modifications in the elevated-temperature-reduction concept wherein the steel is. subjected to a cold reduction step in advance of the elevated temperature reduction, wherein the steel is given a normalized structure, as by normalizing the steel, prior to advancement of the steel through the die to effect reduction in the cross-sectional area while the steel is at an elevated temperature, and wherein the steel is subjected to an annealing operation atent D to provide an annealed structure in the steel for advancement in the e1evated-temperature-reduction step. In each of these processes, utilization continues to be made of the characteristics of the steel to strain-harden and to harden by some mode of precipitation when worked at elevated temperature to produce steels having anew and improved combination of properties and characteristics. The processes, described in the aforementioned copending applications and in the applications filed concurrently herewith, the e1evated-temperature-reduction step is carried'out with the hot-rolled steel without effecting a phase. change in the steel prior to or during the elevated-temperature-reduction step.

In a further copending application, filed concurrently herewith, new and improved combinations of properties have'been developed in steel by the combination of steps which includes heating the. steel to austenitizing temperature and rapidly cooling, the steel, as by quenching the steel, to produce a phase change in the steel, tempering the steel and then subsequently processing the austenitized and tempered steel in an elevated-temperatitre-reduction step as described in the aforementioned copending applications,,as, by advancing the. steel through a die to take a reduction in cross-sectional area while the steel is at a temperature within the range of 200 F; to the lower critical temperature (1100l200 F.). It

' has now been found that still further new and novel steel products having new and dilferent combinations of properties and characteristics can be produced when, in the cold-fihishingofthe steel, the steel is heated to austenitizing temperature and rapidly cooled as, for example, by means of an oil or water quench, to produce a phase change in the steel and then subsequently, without tempering the quenched steel, taking an elevated-temperature reduction as described in the aforementioned copendingapplications as by advancing the steel through, a die to elfect reduction in cross-sectional area while the steel isat an elevated temperature within the range of 200 F. to the lower critical temperature for the steel composition. In most instances, the lower critical temperature. will lie closely'to a temperature within a range of 1100- 1200 F.

Included among the physical and mechanical. prop.- erties influenced by processing steels in the manner d'e scribed are the strength properties of the steel, including; tensile strength, impact strength, yield strength, fiexural strength, and the like, and other propertiessuch' as e1asticity, elongation, hardness, surface roughness, machinability, proportional limits, and the like. The more significant improvements secured in steels processed in the manner embodying features of this invention reside in the higher elastic and impact-strength properties produced in the steels without loss of the high strength levels which are secured by eleVated-temperature-reduction, as

described in the aforementioned copending applications. The same phenomena of the improvements 1n physical and mechanical properties of steels secured by reduction temperature except that a broader range of properties is for the steel, and preferably at a temperature within the range. of 200-800" F.

The characteristics described are capable of d'velopment with hot-rolled steels of the type which are generally cold-finished by the processes of drawing or extrusion. Steels which may be used in the practice of this invention are of the type which strain-harden or harden bysome mode ofprecipitation in hot-rolled condition when worked at'an elevated temperature. Representative are the easy-to-draw steels or non-austenltlc steels'having a pearlitic structure in a matrix of free ferrite. These may .be distinguished from the hard-todraw, high-speed, or carbon-tool steels, or the high-alloy steels and stainless steels. In the process of austenitlzing and. quenching, the-structure of the steel is converted to one that contains either bainite or martensite, aloneor incombin'ation. The austenitized'and quenched steel is relatively hardto draw at room temperature but can be drawn or otherwisereduced in cross sectionwhenthe reduction step is taken while the steel is at an elevated temperature within the range described of from 200 F. to the lower critical temperature for the steel composition, and preferably while at a temperature within the range of 200900 F.-

In the'process embodying the features of this invention, the temperature of the steel in the elevated-tem perature-reduction step, the chemistry of the steel and the'am'ount of reduction that is taken in the steel have influence on the combination of characteristics and properties that are capable of being developed in the steel product. By the proper selection of temperature; chemistry, and reduction, it is'possible to produce steels havmg widely varying physical and mechanical properties,

and it is possible selectively to produce steel products having desirable and low stress characteristics thereby to produce new and improved steels having new and different applications and having combinations of characteristics which differ substantially from the steels processed by the other methods described in the aforementlon'ed copending applications, and to produce 'steels having characteristics and properties which differ from steels of the type which have heretofore been produced by various other techniques.

' Treatment of the steels after the elevated-temperaturereduction step, as byslow cooling in air or by quenching rapidly to cool the steel, has very little effect upon the characteristics and properties developed in the steel,'with the exception that rapid cooling tends more to produce steels having lower levels of stresses and tends to produce steels having a preponderance of compressive stresses to provide steels characterized by compressive warpage. As used herein, the term elevated temperature .reduction 1s meant to include the step of cold-finishing steels wherein the steel is adva a draw die, extrusion die, or roller die, to effect reductron in cross-sectional area while thesteel is at a temperature within the range of 200 ,F. to the lower critical temperature for the steelcomposition, and preferably at a temperature within the range of 200900 F. While non-equivalent'from the standpoint of the process, many of the characteristics described are also capable of being'developed by other processes for working steel to effect reduction in cross-sectional area while thesteel is at the desired elevated temperature, such, for example, as by the process of rolling steels to effect reduction in cross-sectional area while the steel is at an elevated temperature within the range described.

The phrase austenitizing and quenching is means to relate to the usual meaning of the term as employed in the steel trade and as defined in the steel handbooks. Briekly described, it relates to the step of heating the steel to austenitizing temperature for. the steel composition, usually within the range of 1500l600 F., followed by rapid cooling of the steel to room temperature, as by means of an oil quench or water quench to freeze the phase change which has beengm'ade to. take. place need through a die,'as in 4 in the steel. The steel product of the austenitizing and quenching step is believed to be formed of a structure which contains bainite or martensite, or eombmauons thereof.

In subsequent portions of this description, data will be given of the properties developed by the processing of steels in accordance with the practice of this invention. The advantage of quenching, as compared to aircooling after drawing, or otherwise reducting the steel in cross-section in the elevated-temperature-reduction step, appears to reside principally in reduction in the residual stress characteristics when use is made of a temperature in the upper range, preferably above 750 F. in the elevated-temperature-reduction step. As a result, it will be expedient, in the following data, to illustrate the differences as between air-cooling and quenching in but a few of the examples, it being understood that similar reduction in stresses and warpage will be secured in other steels processed at equivalent temperature in the elevatedtemperature-reduction 'step. I 7

The concepts of this invention will be illustrated by reference to the processing of four steels which may be taken as representative of the classes of steels that can be employed. These representative steels will be referred to as C-10l8, C-1144, 0-1080, and 4140 steels. The following is a ladle analysis of these steels, in which the major ingredients, other than iron,' are set forth:

Chemistry Grade 0 Mn rfs s1 Cr Procedure heated to the following temperature:

While at austenitizing temperature, the steels were quenched for rapid reduction of their temperature to ambient temperature by immersion inan oil bath. It will .be understood that other means'for rapidly cooling the austenitized steel to ambient temperature may be employed and that such othermeans are well known to thetrade. p I v The austenitized and quenched steels were drawn at room temperature for the development of comparative data in a cold reduction step, While others of the austenitized and quenched steel bars were rerheate d to the desired elevated temperature for advancement through the die in the elevatedetemperature-reduction step. For suchpurpose, the austenitized and quenched steel bars can be re-heated in agas-fired furnace or other suitable heating furnace employed in the metal art. In the development of the data, reduction in cross-section at elevated temperaure was effected by advancing the steel through a draw die to effect the desired reduction in cross-sec and at the temperatures of drawing and the amount of reduction were kept-as uniform as possible In the development of the data, steels of the following diameters were used:

The terms employed in the presentation of data have the usual meaning in the metal art, with the exception possibly, of the term 'warpage factor. Warpage factor is directly related to residual stress. The warpage value is an indication of the concentration and character of the longitudinal stresses present in steel. The residual stress is obtained by means of a warpage test wherein the length of the test piece is determined as being five times the diameter plus two inches. The test pieces are slotted through a diameter for a distance five times the diameter of the piece. The length of the slot is recorded and the maximum diameter perpendicular to the slot is also recorded- The difierences between the diameter before slotting and after slotting represents the flare caused by the presence of residual stresses. The flare is considered positive, indicative of a preponderance of tensile stresses in the steel, if the bar expands upon slotting. The flare is considered negative, indicative of preponderance of compressive stresses in the steel, if the ends move toward the cut made through the diameter. The warpage values determined for evaluation are calculated on the following equation:

Warpage factor= where Table I [0-1018: Austenitized at 1600 F. Reduced 17.2% before drawing. Air-cooled after drawing] Tensile Yield Elonga- Red. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F.,

Ft.-Lbs. I

Hot R011 1 68, 375 46, 875 36. 0 67. 9 021 87. 0 151 Hot R011 1 as Quenched- 164,000 109, 500 11. 5 22. 6 400 17. 0 371 295 225, 000 198, 000 1. 4 2. 0 322 8. 0 448 189, 000 183,000 1. 4 1.0 +.012 3.0 458 156,750 155,000 9. 5 15.0 -.034 5.0 343 163, 500 162, 500 11. 5 25. 5 052 8.3 336 133, 500 13, 500 14. 5 53. 7 012 26. 0 296 115, 000 108, 500 21.0 66.6 023 2 69. 7 258 95, 500 84, 000 24. 5 67. 9 017 2 77. 0 213 94, 000 79, 000 28.0 72. 0 029 2 113.0 226 1 Not drawn Table II [0-1018: Austenltized at 1600" F. Reduced 17.2% before drawing. Quenched in water after drawing] Tensile Yield Elonga- Red. 01' Izod Hardness, Temp. 01' Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

' p.s.i. p.s.i. Percent Percent Factor 70'F., M

Ft.-Lbs.

Hot Roll 1 68, 375 46, 875 36. 0 67. 9 021 87. 0 151 Hot R011 1 as quenched. 164, 000 109,500 11. 5 22. 6 400 17. 0 371 290 163, 500 162,000 5. 0 23. 1 328 5. 7 336 157, 000 156, 000 5. 0 22. 6 449 8. 7 336 158, 500 157, 500 8.0 16. 5 058 13. 3 291 178, 500 178, 500 3. 5 9. 1 058 7. 3 402 130, 500 129,000 11.0 43. 6 10.0 336 113, 500 105, 000 21. 0 58. 1 086 2 65. 7 249 100,000 85, 500 27. 5 70. 7 121 1 99. 0 220 100, 500 85, 000 27. 5 65. 3 275 2 106. 3 213 1 Not drawn.

1 Averaged values for a fibrous iracturenot a clean break test.

Table III [Cl-1018: Austem'tized at 1600 F. Reduced 30.8% before drawing. Air-cooled after drawing.)

, Tensile Yield Elonga- Red. of Izod Hardness, Temp. 01 Draw, F. Strength, Strength, tion, 1.4", Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent. Factor 70 F., MR

Ft.-Lbs.

Hot R011 G8, 375 46, 875 36. 0 67. 9 +.021 87.0 151 Hot R011 1 as Quenched. 164, 000 109, 500 11. 5 22. 6 400 17. 0 371 .LNot drawn.

' 1 Averaged values for a fibrous structure-not a clean break test.

. Table IV [Ci-1018: Austenitized at 1600 F. Reduced 30.8% before drawing. Water-cooled after drawing.]

, Tensile Yield Elonga- Red. of Izod Hardness,

Temp. of Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F., MR

. Ft.-Lbs.

1 Not drawn. I Averaged values for a fibrous structure-not a clean break test.

Table V [(3-1144: Austenitized at 1500 F. Reduced 21.6% before drawing. Air-cooled after drawing.]

Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Drew, F. Strength, Strength,- tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F., MR

Ft.-Lbs.

. Table VI [ti-1080: Austenitized at 1500 F. Reduced 15.7% before drawing. Air-cooled after drawing.]

Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Drew, F. Strength, Strength, tion, 1.4", Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor F., MR

Ft.-Lbs.

Hot Roll 1 144, 500 76, 000 12. 5 17 0 025 4. 7 206 Hot Roll 1 as Quenched- 061 2.0 436 064 4. 3 490 163 7.0 479 124 11. 0 502 070 11. 7 438 039 18. 7 364 023 26. 3 330 1 Not drawn.

2 Estimated from averaged hardness values of quenched specimens-Materiai appears to be very brittle and difiicult to machine in the as quenched condition.

Table V11 [4140: Austenitized at 1550" F. Reduced 19.9% before drawing. Air-cooled after drawing.]

Tensile Yield Elonga- Red. 01 Izod Hardness, Temp. oi Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F., MR.

Ft.-Lbs.

Hot Roll I 140,000 105, 750 15.0 42.8 004 9.0 307 Hot Roll 1 as QuenchecL- 286,000 231,000 12.1 42. 8 409 25. 7 448 630 324, 250 318,000 8.0 25.0 478 8.3 610 244, 000 243, 750 4. 3 16. 0 427 21. 3 490 198, 500 196,000 10. 0 36. 2 210 36. 7 429 187,000 178,750 14.0 50. 9 +.096 43.3 402 158, 250 151, 250 18.0 59. 5 045 2 73. 7 336 1 Not drawn. Averaged value for a fibrous structurenot a clean break test.

It will be apparent from the foregoing data that the parabolic curve characteristic of the improvements in strength properties developed by elevated temperature reduction, as described in the aforementioned copcnding at least through the central portion of the elevatedtemperature range.

In many instances, the austcnitizcd and quench-hardened steels could not even be drawn to eifect reduction applications, is also capable of development in steels 70 in cross-sectional area while at room temperature, whereprocessed with the combination of steps embodying the features of this invention. The steels which are austenitized and quenched and then reduced at elevated temperature are capable, by the elevated-temperature-reducas the steels could be reduced in cross section when further processed in accordance with the teaching of this invention by taking the elevatedtemperature-reduction step. Improvements have been experienced in the tensiletion step, to provide the increase in strength properties, strength properties in the austcm'tized and quench-hardened steels drawn at elevated" temperature when compared to the strength properties developed in the same steels drawn at room temperature for an equivalent reduction. The improvements in tensile strength and other strength properties appear to be maximized in the range of 400- 850 F., and more broadly Within the range of 200900 F. The same type of improvements is secured in yield strength, hardness, and ductility, as measured by percent elongation and reduction in area, without limitation as to air-cooling or quenching the steels after the elevatedtemperature-reduction step. The range of properties of the austenitized' and quench-hardened steels which are reduced at elevated temperature differs from those capable of being developed by elevated-temperature reduction alone of hot-rolled steels. In addition, improvements are secured in machinability.

The data which will hereinafter be set forth compares the properties capable of being developed in steels processed in accordance with the practice of this invention with the properties available in the same steels during various stages of the process and with other methods for processing to take an equivalent reduction at equivalent temperature, as in the elevated-temperature-reduction process of the aforementioned copending applications. In the presentation of data in the following tables, the values have been arbitrarily selected as the better of the values for the respective properties processed within the described temperature range. For example, higher tensile strengths and yield strengths are available in steels drawn at temperatures within the range of about 200- 900 F while the higher values of elongation and reduc tion in area are developed in steels drawn at temperatures within the upper portion of the elevated temperature-reduction range.

In the tables, the following abbreviations have been, used:

Table VIII (0) At 545 F. (9) At 580 F.. (b) At 1000 F. h) At 920 F (c) At 450 F. (1) At 530 F. ((1) At 380 F. (j) At 930 F. (e) At 1030 F. (1:) At 690 Total Tensile Yield Elonga- Red. of Warpage Izod Hardness, Process Red, Strength, Strength, tlon, 1.4", Area, Factor Impact, DPN,

Percent p.s.i. p.s.i. Percent Percent Range 70 Fl, MR"

Ft.-Lbs.

68, 375 46, 875 36. 0 67. 9 021 87. 0 151 103, 000 3, 000 13.0 52. 1 003 23. 0 223 116, 250(0) 116, 250(0) 27. 5(0) 58. 8(0) 001- 184 11. 7 (c) 266 Hot R011 as Quenched..- 164, 000 109, 500 11. 5 22. 6 400 17. 0 371- AQCD(A) 17. 2 225, 000 198, 000 1. 4 2. 0 322 3. O 448 A D(A) 17.2 189, 00001) 183, 000(d) 28. 0(8) 72. 0(e) 012- 052 26.00) 458, Cold Drawn (A) 30.8 2,000 112, 000 11.5 48; 9 019 17. 3 249v D(A) 30. 8 129, 250(0) 129, 250(9) 20. 00!) 52. 5(h) 057-. 121 38 0(0) 271 AQOD(A) 30. 8 1, 0, 500 5. 1 17.0 535 6 0 324. D( 30. 8 19s, 500(1) 198, 500(1) 26.00) 66.3(]') 369 +.013 21 00) 438 Table IX (0) At 660 F. (d) At 960 F (b) At 940 F. (a) At 920 F (0) At 500 F. (I) At 520 F Total Tensile Yield Elonga- Bed. of Warpage Izod Hardness, Process Red, Strength, Strength, tlon, 1.4, Area, Factor Impact, DPN, Percent p.s.i. p.s.i. Percent Percent Range 70 F., MR

Ft.-Lbs.

Hot RolL. 108.000 70, 500 23. 0 46. 1 004 32. 7 220- 21 6 2, 750 118, 750 13.0 34. 4 732 18. 0 266 21 6 150, 250(0) 000(0) 15. 0(0) 42. 3(0) 711- 170 35. 3(0) 318 246, 9, 00 0.7 4.0 184 8. 0 450 21. 6 294, 000 (c) 267, 000 (ll) 27. 5((1) 52. 1 ((1) +1. 333- 021 55. 0(d) 526 21. 6 133, 00 9. 0 31. 2 789 22. 3 258 21. 6 152, 250 (a) 147, 500((1) 16. 0(0) 40. 6(0) 740- 050 32. 0(6) 324 21.6 301, 0(1) 8, 000( 19. 5(d) 51. 7(d) +1.127-0 48. 0(d) 600 Table X (a) At 610 F (d) At 600 F. (b) At 940 F (e) At 900 F. (c) At 815 F Total Tensile Yield Elonga- Red. of Warpage Izod Hardness, Process Red., Strength Strength, tion, 1.4, Area, Factor Impact, DPN,

Percent p.s.i. p.s.i. Percent Percent Range F., MR

- Ft.-Lbs.

144, 500 76, 000 12. 5 17.0 025 4. 7 296 t 170, 500 148, 500 5. 0 14. 5 077 3. 3 324' 189, 000(a) 186, 000(a) 10. 0(0) 12. 4(1)) 077- 038 5. O(c) 378 Hot Roll as quenched... 204, 000 -.061 2.0 436 15. 7 337, 000(d) 315, 000(d) 14. 5(6) 34. 4(0) 163- 064 26. 3(e) 490 Table XI (a; At 595 F. (d) At 1010 F.

At 960 F At 916 F. (0) At 630 F Total Tensile Yield Elonga- Red. of Warpage Izod Hardness, Process Red., Strength, Strength, tion, 1.4", Area, Factor Impact, DPN,

Percent p.s.i. p.s.i. Percent Percent Range 70 F., MR

Ft.-Lbs.

140, 000 105, 750 15. 0 42. 8 004 9. 0 307 165,000 162,000 9.0 44.0 +.083 4.3 336 ETD(A) 189, 500(41) 189, 000(a) 16. (0) 49. 4(0) 211- 064 15. 0(b) 394 H015 Roll 35 quenched- 286, 000 231, 000 12. 1 42. 8 409 25. 7 448 AQD(A) 19. 9 324, 250 (c) 318, 000(0) 18. 0(d) 59. 5(11) 478- 045 43. 3(a) 610 From the foregoing data, it will be apparent that in many of the properties, particularly in the strength properties and in the properties which indicate elasticity, considerable, improvement is secured by the combination of steps which includes austenitizing and quenching followed by reduction in cross section at elevated temperature when compared to the system for processing steels by the use of an elevated-temperature-reduction step alone. Itwill be apparent also that the improvements are made available without limitation by means of treating the steel subsequent to drawing, as by air-cooling or quenching, and it will be evident further that the foregoing improvements can be developed in the steel in which high reductions are taken as well as low reductions. The improvements in residual stress characteristics follow the same general pattern as are made available by the elevated-temperature-reduction step, whether austenitized and quenched prior to reduction or whether reduction is taken on the hot-rolled steel without previous treatment.

By the combination of steps comprising austenitizing and quenching to effect a phase change followed by reduction at elevated temperature, steels having new and improved characteristics and new combinations thereof can be secured with particular emphasis on improvements in elasticity, machinability, strength properties, and hardness.

It will be understood that changes may be made in the details of processing the steel and its method of handling without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. The metallurgical process for improving the characteristics of steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite comprising the combination of steps of austenitizing the steel and quenching the austenitized'steel to effect a phase change to martensite and then advancing the martensitic steel through a draw die to effect reduction in cross-sectional area in a drawing operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

2. The metallurgical process for improving the characteristics of steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite comprising the combination of steps of austenitizing the steel and quenching the austenitized steel to effect a phase. change to martensite and then advancing the martensitic steel through an extrusion die to elfect reduction in crosssectional area in an extruding operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

'3. The metallurgical process for improving the charbination of steps of austenitizing the steel and quenching the austenitized steel to efiect a phase change to martensite, and then working the martensitic steel to effect reduction in cross-sectional area while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

4. The metallurgical process for improving the characteristics of steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical tem perature for the steel composition comprising the comb1- nation of steps of austenitizing the steel, quenching the austenitized steel to form martensite and then advancing the martensitic steel through a draw die to efiect reduction in cross-sectional area in a drawing operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel compositron.

5. The metallurgical process for improving the characteristics of steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of austenitizing the steel, quenching the austenitized steel to form martensite and advancing the martensitic lsteel through an extrusion dieto eifect reduction in cross-sectional area in an extrusion operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

6. The metallurgical process for improving the characteristics of steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of austenitizing the steel, quenching the austenitized steel to form martensite and'then rolling the martensitic steel to efieot reduction in cross-sectional area in a rolling operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

7. A steel product having new and improved characteristics produced by the method of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,018,369 Potter Feb. 20, 1912 2,435,511 Rice Feb. 3, 1948 2,448,753 Weesncr Sept. 7, 1948 OTHER REFERENCES 

3. THE METALLURGICAL PROCESS FOR IMPROVING THE CHARACTERISTICS OF STEEL WHICH STRAIN-HARDENS AND WHICH HARDENS BY SOME MODE OF PRECIPITATION WHEN WORKED AT A TEMPERATURE BETWEEN 200*F. AND THE LOWER CIRTICAL TEMPERATURE FOR THE STEEL COMPOSITION COMPRISING THE COMBINATION OF STEPS OF AUSTENITIZING THE STEEL AND QUENCHING THE AUSTENITIZED STEEL TO EFFECT A PHASE CHANGE TO MARTENSIT, AND THEN WORKING THE MARTENSITIC STEEL TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA WHILE THE STEEL IS AT A TEMPERATURE WITHIN THE RANGE OF 400*F. TO THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION. 